Process of making brake drums



April 1934. A. BOEGEHOLD Er AL I 1,953,925

PROCESS OF MAKING BRAKE DRUMS Filed Feb. 28, 1931 HIGH MANGANESE STEEL.

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dummy Patented Apr. 10, 1934 UNITED STATES PATENT OFFICE PROCESS OF MAKING BRAKE DRUMS poration of Delaware Application February 28, 1931, Serial No. 519,010

2 Claims.

This invention relates to brake drums and particularly to an improvement in the process of making such drums as are used on vehicles.

An object of the invention is to prevent the scoring of the brake drums.

This object is attained by making a brake drum of steel having a comparatively high content of manganese and carbon between'0.20% and 35%.

A further object is to condition such a manganese steel so that it may be formed into brake drums without cracking in the process of shaping.

Other objects will appear from the following description:

The single figure of the drawing shows in section a brake drum made from high manganese steel.

It has been customary in forming brake drums from sheet steel containing over 0.20% carbon to use sheets having a manganese content of less than .40%. This limit is determined by the embrittling action of the pickling treatment to which the sheet is subjected immediately before forming. Steel having more than 0.40% manganese is so embrittled by pickling that it tends to crack when shaping to form a brake drum while cold. To avoid the cracking the material may be formed while hot, but the expense of hot forming is such that this method of forming drums is regarded as not commercial.

An unexpected result has been discovered when steels having a higher manganese content are used. It has been found that such drums are much more resistant to scoring when frictionally engaged by harsh brake linings. If, therefore, a steel could be used having a high manganese content, much better results would be obtained and linings would be available of better frictional properties than can be used with steel having a low manganese percentage While improved results are obtained with steel having manganese slightly in excess of the aforesaid .40%. very striking results have been obtained with steel containing 1.60% or more of manganese. It is belived that from .40% to 2.00% may represent a reasonable statement of the range which is productive of the improvement in brake drum steel.

It is therefore the purpose of this invention to make brake drums of steel containing manganese ranging from .40% to 2.00% for the purpose of avoiding scoring. To facilitate the shaping of such drums from steel having these high percentages of manganese, it has been found advantageous to subject the sheet steel to a preliminary heat treatment. Sheets of high manganese steel are heat treated to about 1700" F.

They are then allowed to soak for some time and then cooled in the furnace. This treatment softens the sheets and in addition, by decarburization, produces a layer of low carbon steel at the surface. The sheet must then be pickled to remove annealing scale. For this pickling step there may be used a 5 to 10% solution by weight of sulphuric acid, the solution being properly inhibited. The pickling process produces some embrittlement due to absorption of hydrogen from the pickling bath. This is removed by a subsequent heating. The heating may be performed at a temperature preferably between 800 and 850 F. The annealing treatment and the reheating after pickling renders it possible to shape the drums while cold without danger of developing cracks.

The invention therefore contemplates (1) the manufacture of drums from steel containing more than 0.20% carbon and having manganese in excess of .40%, (2) it contemplates a preliminary heat treatment of the sheets to make them soft and to remove the carbon in the surface layers, and (3) the elimination of the brittle condition resulting from pickling whereby the drums may be formed from the material while cold without danger of cracking.

We claim:

1. The process of making brake drums from a steel sheet having a content of manganese between.40% and 2.0% consisting in softening the sheet and decarburizing its surface, removing surface scale and shaping said sheet while cold to the form of a drum.

2. The process of making brake drums from a steel sheet having a content of manganese in excess of .40% consisting in softening the sheet and decarburizing the surface, pickling the sheet, reheating to remove embrittlement and shaping the sheet while cold to the form of a drum.

ALFRED L. BOEGEHOLD. CLARENCE J. TOBIN. 

